1. Field of the Invention
The present invention relates to a thermal-assisted magnetic recording head and more particularly to a thermal-assisted magnetic recording head which heats a recording bit by irradiation in recording data into a magnetic storage medium and a magnetic recording apparatus provided with the recording head.
2. Description of Related Art
In recent years, as storage media for storing information, various types of high-density magnetic storage media have been developed. These high-density magnetic storage media have a problem that the magnetic bits are significantly influenced by temperature, and the storage media must have high coercive force. The magnetic field used for recording data into the storage media having high coercive force must be strong. The upper limit of the strength of the magnetic field generated by a recording head depends on the saturation magnetic flux density. At present, the upper limit of the magnetic field strength is almost the limit determined by the material, and a large increase in the magnetic field strength cannot be expected any more.
As a countermeasure, a thermal-assisted magnetic recording method has been suggested. In the thermal-assisted magnetic recording method, immediately before a start of recording, a storage medium is partly heated, so that the magnetic force of the heated part of the storage medium becomes weaker. Then, recording is performed while the coercive force of the storage medium is weaker. Thereafter, the heated part naturally cools down, and magnetization of the recorded magnetic bits can be stabilized.
In the thermal-assisted magnetic recording method, the heating of the storage medium is preferably performed instantaneously, and a heating device is not allowed to be in contact with the storage medium. For the heating, usually, a method using light absorption is adopted. In the case of high-density magnetic recording, however, the diameter of the spot to be heated is approximately 20 nm, and because of diffraction limit, it is impossible to converge light on the very small spot by use of an ordinary optical system using propagated light.
In order to solve this problem, Japanese Patent Laid-Open Publication No. 2005-116155 (reference 1) suggests a method wherein near field light, which is not propagated light, is used for the heating. In the method, a laser beam with an appropriate wavelength is converged on a metal film with a size of several tens of nanometers (a plasmon probe) by an optical system, so that near field light (localized plasmon) is generated, and the near field light is used as a device for heating the recording bit.
In a magnetic recording apparatus, a storage medium is placed in a small space, and a recording head is inserted into a space not more than 1 mm. Therefore, it is almost impossible to arrange a light source and an optical system for irradiating the storage medium above the recording head, which is implemented by the optical/magnetic data storage apparatus disclosed by the reference 1. Then, in the magnetic recording apparatus, a very thin light directing device and a very thin light converging device are required.
Sharp Technology Report, Vol. 91, pages 26-30 discloses a method wherein a recording bit is heated by near-field light generated by a very small aperture laser. In this method, however, the laser must be arranged in proximity to a plasmon probe, and the fixing method and the wiring are complicated. Also, it is necessary to arrange a magnetic recording head and a near-field generator in proximity to each other, while it is necessary to consider physical interference between the laser and the recording head. In this method, therefore, it is impossible to make use of the feature of irradiation that a light emitting point and an irradiating point can be distant from each other.
Japanese Patent Laid-Open Publication No. 2000-149317 discloses that light is converged by a reflective mirror so as to generate near-field light, and Japanese Patent Laid-Open Publication No. 2000-353336 discloses that near-field light is generated by use of a beam splitter and an elliptic mirror. In these structures, however, optical elements, such as a collimator lens, an elliptic mirror, etc., are further necessary so as to direct light from the light source into the head. Accordingly, the optical system becomes thick, and it is difficult to employ these structures for the thermal-assisted magnetic recording apparatus.